Why the colonials call Petrol and Gas?
Why do colonials call Budweiser a beer as well?
Why am the English always bringing this up?
We call gasoline gas, it's just short for gasoline.
Why do the english call gasoline petrol (short for petroleum)? I could easily confuse your word for car fuel with Diesel, kerosene, butane, propane, fuel oil, tar and even asphalt (which you call tarmac).
The more important question regarding Budweiser is "why do people bother drinking Budweiser?"